The long-term goal of this project is to understand some of the basic mechanisms underlying the cellular degeneration which is a major feature of several neurological disorders, including Parkinson's (PD) and related diseases. The dopaminergic neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces an animal model of PD. The actual toxic agent in producing a lesion in the substantia nigra is thought to be its metabolite, 1-methyl-4-phenylpyridinium (MPP+). In this proposal various aspects of the hypothesis that MPP+ acts to kill cells by inhibiting mitochondrial metabolism at Site 1 of the electron transport chain will be further examined. It has been suggested that PD and some other degenerative disorders involve an abiotrophic interaction of aging and environmental factors. Therefore, the effects of MPTP/MPP+ on preparations from aged mice will also be studied. Specifically, the uptake of 3H-MPP+ by mitochondria will be measured in the presence of various analogs of MPP+ as well as in the presence of other organic cations such as chloroquine. The effect of these substances on the MPP+- induced inhibition of Site 1 respiration will also be studied. Mitochondria from synaptic endings will be compared to "bulk"- isolated brain mitochondria as well as liver mitochondria. These experiments will furnish important information as to the nature of the membrane carrier system for MPP+ and similar cations. The inhibition of aerobic glycolysis by MPTP, MPP+ and their analogs will be studied in tissue slices and synaptosomes from striatum and other brain areas. MAO-A/B inhibitors and dopamine uptake blockers will be used with these analogs to determine which factors (metabolism, uptake or mitochondrial inhibitory potency) are the principal determinant of inhibition. Using fluorescence probes, the effects of MPTP/MPP+ on intracellular free calcium concentration and mitochondrial membrane potential will be correlated with actual cell toxicity. The studies on effects of MPTP/MPP+ on mitochondria, tissue slices and synaptosomes will be compared in preparations from mice of different ages, including aged mice.